1. Field of the Invention
The present invention relates generally to a sheet processing apparatus and an image forming system and, more particularly, to a binding mechanism for media sheets, on which images are formed.
2. Description of the Related Art
Postprocessing, such as binding using a stapler, is performed on a stack of a certain number of sheets of printout produced by an image forming apparatus in some cases where the printout sheets are not directly ejected from the image forming apparatus. Examples of the image forming apparatus include a copier, a printer, and a printing apparatus. As a device for this purpose, a sheet processing apparatus connected to a sheet ejecting unit of the image forming apparatus is typically employed.
Although binding using staples is popularly performed, devices that do not consume metal items, such as staples, have been desired in recent years from the viewpoint of resources saving, ecology, and recyclability.
Examples of such a device include binding devices disclosed in Japanese Laid-open Patent Application No. 2010-208854 and published Japanese translation of a PCT application 2007-536141. The binding devices bind a stack of sheets together by applying deep-nested embossment on the sheet stack using toothed jaws capable of pinching and pressing the sheet stack.
In a conventional configuration for binding, a top land of a toothed jaw has what is referred to as a sharp-edged corner, which is a corner shaped like a ridge formed with intersecting straight lines. Accordingly, there can arise a problem that when such toothed jaws are brought into mesh to perform binding, they can undesirably cut fibers of paper, whereby binding strength is decreased.
Meanwhile, disclosed in published Japanese translation of a PCT application 2007-536141 is forming rounded ridges on corners of top lands of protrusions for use in embossing.
However, this configuration adopts round corner edges, each approximating an arc shape obtained by removing a corner edge with one or more straight lines or an irregular cut line, in order to increase wet burst strength of a product, such as tissue paper.
Meanwhile, making sheets incapable of recovering to their original shape by bending and permanently deforming a corner of ridged-and-grooved surfaces can be one of measures for preventing sheets that are bound by deep-nested embossing from becoming apart.
From this standpoint, the configuration disclosed in published Japanese translation of a PCT application 2007-53614 focuses only on an aspect that the wet burst strength of a product is affected by an embossment height, and does not consider about preventing a decrease in binding strength by preventing bound sheets from recovering to their original shape.
In light of the problem pertaining to the conventional sheet processing apparatuses, there is a need for a sheet processing apparatus configured to be capable of binding sheets by applying deep-nested embossment without causing fiber breakage of the sheets.
It is an object of the present invention to at least partially solve the problem in the conventional technology.